Drilling apparatus and method for producing a bore

ABSTRACT

A drilling apparatus and a method for producing a bore in a bottom of a body of water from a floating platform that is exposed to lifting motions, such as a wave motion. The drilling apparatus includes a carrier device, a drill string substantially vertically displaceable in an axial direction along the carrier device, a drilling drive for applying torque to the drill string, and a control unit designed to control and reduce the torque of the drilling drive during drilling operation to a threshold value at which the at least one drill string element is further axially displaceable to compensate for lifting motions when there is friction on a contact surface. The drill string includes at least one axially displaceable drill string element and at least one axially extending abutment strip that is in engagement for torque transmission with the formation of the contact surface.

The invention relates to a drilling apparatus for producing a bore in the bottom of a body of water from a floating platform which is exposed to lifting motions, in particular a wave motion of the body of water, with a drilling drive for applying a torque, a drill string comprising at least one drill string element, which is displaceable in the axial direction relative to the drilling drive and comprises at least one abutment strip extending in axial direction, which is in engagement with the drilling drive and/or at least one abutment strip of an adjacent drill string element for torque transmission for the formation of a contact surface, and a carrier device along which the drill string is substantially vertically displaceable.

The invention furthermore relates to a method for producing a bore in the bottom of a body of water from a floating platform which is exposed to lifting motions, in particular a wave motion of the body of water, in which a drilling drive applies a torque to a drill string, wherein the drill string comprises at least one drill string element which is displaceable in an axial direction, the torque is transmitted from the drilling drive and/or an abutment strip of an adjacent drill string element by means of at least one abutments strip extending in the axial direction, whereby during the drilling operation a contact surface is formed at the at least one abutment strip.

Bores in the bottom of a body of water can be easily implemented by a drilling apparatus from a floating platform, in particular a ship, a pontoon or a floating barge. In case of the floating platform undesired motions of the drilling apparatus relative to the bore hole may occur, which is problematic for a secure and precise implementation of the bore. The motions can thereby occur in parallel and/or perpendicularly to the bore hole axis. The motions of a floating platform that can be exposed on a body of water in particular to wave motions and/or tidal movements can be several decimeters to some meters high.

In order to balance out wave motions, it is known from EP 1 103 459 A1 or U.S. Pat. No. 5,209,302 to provide controlled positioning cylinders. However, construction-wise this is very complex. Further drilling devices with compensators for balancing out wave motions are disclosed in U.S. Pat. No. 3,917,006 A or U.S. Pat. No. 3,653,636 A.

For producing a bore in the bottom of a body of water often a kelly drilling method is applied. In this drilling method, a drilling apparatus with a kelly bar is used, which is a telescopic boring bar. The kelly bar, at which a drilling tool is located in a lower area, can thereby compensate length variations during the drilling operation.

In case of a floating use of the kelly drilling method for drilling in the bottom of a body of water from a floating platform, problems with the wave motions may occur as well, if the axial displacement is blocked. If the distance between the borehole bottom or the drilling tool, respectively, and the drilling apparatus caused by wave motions is reduced, a high bending load of the kelly bar may occur in the drilling operation. This problematic bending stress may lead to an overstress of the telescopic drill string that is detrimental for the material on the one hand, and on the other hand to an irregular detaching of soil material at the borehole bottom. Even damage in the drilling apparatus and hazard to the platform may occur.

The invention is based on the object of providing a drilling apparatus and a method for producing a bore, in particular in a bottom of a body of water from a floating platform, by which drilling can be implemented particularly efficiently and non-destructive.

On the one hand, the object is solved according to the invention by a drilling apparatus comprising the features discussed below, and on the other hand with a method for producing a bore with the features discussed below.

The drilling apparatus according to the invention is characterized in that a control unit is provided, which is designed to control and reduce the torque of the drilling drive during the drilling operation to a threshold value at which the at least one drill string element is further axially displaceable to compensate for lifting motions when there is friction on the contact surface.

A basic idea of the invention is to compensate relative movements of the drilling apparatus relative to the borehole bottom by a reliable extension and retraction of the drill string. The drill string can be a single rod with only one drill string element or be composed of several drill string elements, in particular through a screw connection. The torque transmission takes place from the abutment elements at the drilling drive to the abutment strips of the drill string. The invention is thereby based on the finding that during the drilling operation high compression forces are exerted on the axial abutment strips in the circumferential direction. This leads to correspondingly high adhesive and friction forces, so that an axial displacement of the drill string element can be blocked. The reliable displacement is achieved according to the invention in that the friction at the contact surfaces of the drill string element is controlled and reduced to an extent that suffices for the method. Thereby, the reduction of the friction is achieved by reducing the torque, which is provided for the compression force and thus the adhesive/friction force at the contact surfaces. The invention constitutes so to speak an ABS system, i.e. an anti-blocking system, for drill strings. In this way it is made possible to reliably compensate for example a lifting motion of the body of water in the axial direction of the drill string. Overstresses are thus avoided. However, the invention can also be applied in drilling onshore.

Lifting motions for the present invention can principally mean all movements in an axial direction of a drill string, which change the distance between a drilling apparatus and a borehole bottom during a bore process. The movements can principally have any amplitude and frequency, though they can be individual, irregular, recurring or periodical. The movements can also be regular and thus predictable, or coincidental. The axial direction may define an axial direction upward and/or downward.

A carrier device of a drilling apparatus as provided in the invention may particularly also be understood as drill mast or as a drill carriage.

A contact surface may exist between the drilling drive and a drill string element and/or between the neighboring drill string elements. These may consist of several contact partial surfaces between the individual abutment strips that are in contact with each other.

A threshold value at which the torque of the drilling drive can be reduced may be zero or even negative in order to shortly counter an undesired torsion. Preferably a torque value is defined with which the friction at the contact surfaces of the drill string is reduced to a sufficient extent in order to compensate for lifting motions.

In the area of the contact surface preferably a means for reducing the friction is provided. This may be the arranging of a friction-reducing material or a particularly smooth-surface processing of the abutment strip. Alternatively or additionally, a lubrication device is provided, which is preferably designed to supply oil or lubricating grease to the contact surface.

A particularly preferred embodiment of the invention is present when a detector unit is provided, which is designed to recognize the lifting motions. The detector unit can thereby be positioned on the floating platform or the drilling apparatus which is located on the floating platform. The detector unit may preferably be a linear acceleration sensor, which particularly determines accelerations in the axial direction of the drill string. From the measured accelerations, speeds and position changes regarding the movements in the axial direction can be determined by integration by the detector unit as such and/or an analysis unit connected to said detector unit. The detector unit may also be located in an immobile place, in particular onshore, and determine the lifting motions. The lifting motions of the body of water that are adjacent to the floating platform can thereby be directly measured, or, preferably, the lifting motions of the drilling apparatus can be directly determined. It can particularly be provided in this respect to observe a measuring mark, which is located on an upper surface of the body of water, or preferably on the floating platform or the drilling apparatus with a position-determining surveying instrument, and in particular to pursue. From position changes conclusions can be drawn to the motions in the axial direction of the drill string.

In a particularly efficient embodiment of the invention it can be provided that the detector unit is coupled with the control unit, and that the torque can be reduced through the control unit when a lifting movement to be compensated is identified by the detector unit. The detector unit can determine occurring lifting motions and communicates that to the control unit. In this respect principally all determined lifting motions can be considered and transmitted, or only those lifting motions which exceed a value that is critical for the drilling operation. Subsequently, the control unit communicating with the drilling drive can reduce the torque based on the transmitted lifting motions. For this, single torques can be allocated to lifting motion values or lifting motion ranges. An infinite adjustment of the torque can take place as well. Particularly preferred is that the lifting motions, in particular those exceeding a predefined threshold value, can be assigned to a torque of zero, which corresponds to a stop of the rotary drive. Recurring, in particular periodic lifting motions by wave motions of a body of water can be predicted by known methods after the motion path was identified by the detector unit, among other things by means of a KALMAN filter. A compensation of such periodic lifting motions can be achieved with a periodic change of the torque. The reduction of the torque can principally take place time or torque-controlled and be adjusted to the lifting motions.

A particularly preferred embodiment variant of the invention is provided in that a drill string is a telescopic drill string with an external drill string element and at least one interior drill string element, in particular a kelly bar. A telescopic drill string, which can be designed with or without locking mechanism for transmitting a force in the axial direction of the drill string, features outer and inner abutment strips forming contact surfaces, in which friction or friction forces, which might occur as adhesive forces or dynamic frictional forces, allow a torque transmission. A change of the occurring friction, which can be in proportion to the applied torque, effects that the drill string can be telescopic adjustably and in reaction to the lifting motions. The drill string can be mounted on a slide, which is fastened in a moveable way to a mast of the drilling apparatus, together with the rotary drive. At a lower end of the string or at the lower end of the internal lying drill string element a polygon profile can be provided, to which a drilling tool is fastened.

According to an enhancement of the invention, a particularly advantageous variant can be achieved in that the telescopic drill string consists of more than two drill string elements, in particular of three or four drill string elements fitted together. The telescopic drill string can be a kelly bar, which consists of an outer kelly, one or more center kellies and an inner kelly. Here, it is particularly preferred to provide two or three center kellies. The drill string elements may comprise several intermeshing abutment strips that are arranged radially offset, which form a contact surface when in each case two adjacent abutment strips are in mutual engagement, whereby the contact surface can be the surface comprising all individual contact surfaces between the abutment strips of the drill string elements.

For detaching soil material, it is particularly expedient, if a drilling tool is arranged at a lower area of one of the interior drill string elements. The drilling tool, which can be a rotary drilling tool, can be connected to the kelly bar by means of a square. The rotary drilling tool can be an auger, a drill bucket or a core drill for example. Erosion tools can be fastened to the drilling tool, which effect a detaching of the soil material. Such erosion tools may consist of, for instance, chisels, shovels or knives.

For compensating of lifting motions, it is provided according to a variant of the invention that the friction at the contact surface between the abutment strings is dynamic friction for compensating the lifting motion. If the friction at the abutment strings for compensating the lifting motions is dynamic friction, a torque can also still be transmitted during the compensation. Consequently, even while compensating the lifting motions by the drilling tool a force can be exerted on the borehole bottom for detaching soil material. It can also be provided that the dynamic friction for compensating the lifting motion is equal zero, which can be caused by stopping the rotary drive. In the process, the stopping can be for a short time period, in particular for less than 1 s.

With respect to the method, the object according to the invention mentioned above is solved in that during the drill drive the torque is controlled and reduced to a threshold value by a control unit, at which value a friction force is produced at the contact surface at which the at least one drill string element is further axially displaceable for compensating a lifting motion. During the compensation of the lifting motion the drilling tool can in particular stay in contact with the borehole bottom, while the drilling apparatus is moving up and down. The torque transmission is thereby adjusted to the lifting motions, in particular reduced.

An advantageous variant of the method according to the invention foresees that the distance between a drilling tool arranged at a lower portion of the telescopic drill strings and the drilling apparatus is changed when compensating the lifting motions. A change of the distance of the drilling tool can correspond to an axial change of the length of the telescopic drill strings. By the change of the distance it can be achieved that a bending of the drill strings is reduced when forces are exerted because of the lifting motions, and that a contact loss of the drilling tool with the borehole bottom is prevented.

It is particularly advantageous for the method when it can be foreseen that the lifting motions are identified by a detection unit and these motions are communicated to the control unit. The control unit, which can be located on the body of water, on the floating platform and/or onshore, to the control can be communicated lifting motions by means of cabled or wireless data transmission. The communicated lifting motions may contain positions, position changes, speeds, speed changes and/or acceleration of the body of water, the drilling apparatus and/or the floating platform.

Another embodiment that is advantageous for the method according to the invention is when drill string is further driven while controlling and reducing the torque. The torque can thereby be reduced to any value greater than zero, whereby a torque can be transmitted further through the abutment string of the drill string. By further driving the drill string, an infinite detachment of soil material and/or pumping out or conveying already detached soil material can be carried out. For this purpose, facilities for pumping or conveying soil material can be provided.

An advantageous implementation of the method can foresee according to the invention that the friction force at the contact surface is a dynamic friction force. The friction force can principally be an adhesive friction force and/or a dynamic friction force. In case of a dynamic friction force it is particularly advantageous that a motion of the telescopic drill string can be allowed as sliding motion in the axial direction, while a transmission of forces for the torque transmission to the drilling tool can still be permitted.

It is particularly expedient for the method when it can be foreseen according to another embodiment variant of the method that an analysis unit is provided, by means of which process data of the torque and the lifting motion are analyzed and documented during the drilling operation. The process data can serve an operator for the visual control or an intelligent analyzing system for an automatic analysis. The method can particularly be optimized in this way. The documentation of the process data can also serve for using process data of already terminated bores in order to reduce and control the torque in further bores within the framework of a knowledge-based information system. This may particularly serve the purpose to increase the progress of removing.

Principally, the occurring torques and the lifting motions during a bore can be arbitrarily recorded and/or illustrated. It can be particularly advantageous that the torques occurring during the drilling operation and the lifting motions are shown in a visual display unit. The visual display can serve a machine operator for monitoring the drilling operation and to evaluate the reaction of the method to occurring lifting motions for the compensation of the same.

According to the invention it is furthermore foreseen to provide a method for producing a foundation element in a bottom of a body of water, whereby at least one bore is produced in the bottom of the body of water and the foundation element is formed in the at least one bore. The method is characterized in that the bore is produced in accordance with the method for producing a bore in a bottom of a body of water from a floating platform. For forming the foundation element, a tube or pile element can be introduced in the bore. Alternatively or supplementary, a backfilling of the bore with a hardenable medium, in particular a cement suspension for forming the foundation element is possible.

Foundation elements can be single pillars or elongated walls in the bottom of the body of water.

The invention is exemplified further hereunder with a preferred embodiment example, which is schematically illustrated in the attached drawings. The drawings thereby show:

FIG. 1 a schematic side view of a drilling apparatus according to the invention on a floating platform; and

FIG. 2 a perspective view of a cut through a drill string along a line A-A in FIG. 1.

An embodiment of a drilling apparatus 100 according to the invention is explained hereunder in connecting to FIGS. 1 and 2.

The drilling apparatus 100 comprises a carrier device 30, a telescopic drill string 10, a drilling drive 40, and drilling tool 42 as main components. The drilling apparatus 100 is placed on a floating platform 4, which can be a pontoon or a ship floating on a body of water 8 with a bottom of a body of water 2. By means of a wave motion of the body of water 8 the floating platform 4, the drilling apparatus 100, and particularly also the drilling drive 40, the telescopic drill string 10 and the drilling tool 42 are moved in an axial direction 6. Said movements can be referred to as lifting motions.

The telescopic drill string 10 is arranged on a slide 34, which is moveable mounted on a mast 32 of the carrier device 30 in the axial direction 6. The telescopic drill string 10 is driven rotatably by the drilling drive 40 at a drill string element 12 arranged on the outside about the rotation axis defined by the axial direction 6. The telescopic drill string 10 comprises a drill string element 12 arranged on the outside, a first internal lying drill string element 14, a second internal lying drill string element 15, and a third internal lying drill string element 16, which are mounted extendible in the axial direction 6. At the third internal lying drill string element 16 a drilling tool 42 is provided at a lower area, which is an auger in this embodiment. The drilling tool 42 has a force-locking connection with the third internal lying drill string element 16 by means of a square connection not shown in the illustration. At the lower end of the borehole in the bottom of the body of water 2 there is the borehole bottom 3. The telescopic drill string 10 can protrude through the floating platform 4 or be passed laterally along the floating platform.

Lifting motions caused by the body of water 8 lead to movements of the floating platform 4 with the drilling apparatus 100 located thereon. In the embodiment these movements are identified by a detection unit 52, which is located on/at the floating platform 4. Movements in the axial direction 6 can thereby occur downwardly in the direction of the bottom of the body of water 2 or upwardly in the opposite direction. The detector unit 52 is connected to the control unit 50 through a data cable 54. The detector unit 52 transfers information to the control unit 50 regarding the movements in the axial direction 6, whereby this information may also contain positions. The control unit 50 can analyze, process and use this information so as to control the drilling drive 40. For this purpose, the control unit 50 is connected to the drilling drive 40 via another data cable 55. The control of the drilling drive 40 through the control unit 50 thereby includes a reducing of the torque from a predefined threshold value as well as the re-increase of the torque of the drilling drive 40 back to the value of the torque existing before the reduction.

The cut A-A plotted in FIG. 1 is illustrated in FIG. 2 from a perspective view. FIG. 2 thereby shows a cut through the extended internal lying drill string elements 14 and 15, whereby the drill string element 15 lies within the drill string element 14. The drill string element 15 in this embodiment comprises two outwardly directed internal abutment strips 22, and the drill string element 14 comprises two inwardly directed external abutment strings 20. When a torque is applied, the external abutments strips 20 are each in contact or in engagement with the internal abutment strips 22, whereby the contact is formed at a contact partial surface 24 each. At the contact partial surfaces 24 friction forces occur in the drilling operation, which can occur as adhesive friction forces or dynamic friction forces. For compensating the motion in the axial direction 6, the contact partial surfaces 24 slide onto each other in the axial direction 6. In case of non-compensation of the motions in the axial direction 6, the contact surfaces 24 adhere to each other for transmitting the torque. 

1. Drilling apparatus for producing a bore in the bottom of a body of water from a floating platform which is exposed to lifting motions, in particular a wave motion of the body of water, comprising a drilling drive for applying a torque, a drill string which comprises at least one drill string element, which is displaceable in the axial direction relative to the drilling drive and comprises at least one abutment strip which extends in the axial direction and is in engagement with the drilling drive and/or at least one abutments trip of a neighboring drill string element for torque transmission with the formation of a contact surface, and a carrier device along which the drill string is substantially vertically displaceable, wherein a control unit is provided which is designed to control and reduce the torque of the drilling drive during the drilling operation to a threshold value, at which the at least one drill string element is further axially displaceable to compensate lifting motions when there is friction on the contact surface.
 2. Drilling apparatus according to claim 1 wherein a detector unit is provided which is designed to identify the lifting motions.
 3. Drilling apparatus according to claim 2, wherein the detector unit is coupled to the control unit and by means of the control unit the torque can be reduced, if a lifting motion to be compensated is identified by the detector unit.
 4. Drilling apparatus according to claim 1, wherein the drill string is a telescopic drill string with a drill string element lying on the outside and at least one drill string element lying on the inside, in particular a kelly bar.
 5. Drilling apparatus according to claim 4, wherein the telescopic drill string is formed from more than two drill string elements, in particular from three or four drill string elements inserted into each other.
 6. Drilling apparatus according to claim 4, wherein at a lower area of one of the drill string elements located on the inside a drilling tool is arranged.
 7. Drilling apparatus according to claim 1, wherein the friction at the contact surface for compensating the lifting motions is a dynamic friction.
 8. Method for producing a bore in a bottom of a body of water from a floating platform which is exposed to lifting motions, in particular a wave motion of the body of water, wherein a drilling drive of a drilling apparatus applies a torque to a drill string, whereby the drill string comprises at least one drill string element which is displaceable in a axial direction, the torque is transmitted by means of at least one abutment strip extending in the axial direction at the drill string element, whereby a contact surface is formed in the drilling operation at the at least one abutment strip, wherein during the drilling operation the torque is controlled and reduced to a threshold value by a control unit, at which a friction force is formed at the contact surface, at which the at least one drill string element is further axially displaceable to compensate a lifting motion.
 9. Method according to claim 8, wherein a telescopic drill string is used, and the distance between a drilling tool, which is arranged at a lower area of the telescopic drill string, and the drilling apparatus is changed when compensating the lifting motion.
 10. Method according to claim 8, wherein the lifting motions are identified by a detector unit and these are communicated to the control unit.
 11. Method according to claim 8, wherein the drill string is driven further during the control and reduction of the torque.
 12. Method according to claim 8, wherein the friction force at the contact surface is a dynamic friction force.
 13. Method according to claim 8, wherein an analysis unit is provided, by which process data of the torque and the lifting motion are analyzed and documented during the drilling operation.
 14. Method according to claim 8, wherein the torques and lifting motions occurring during the drilling operation are shown in a visual display unit.
 15. Method for producing a foundation element in a bottom of a body of water, wherein at least one bore is produced in the bottom of a body of water, and in the at least one bore the foundation element is produced, wherein at least one bore is produced in accordance with a method according to claim
 8. 